I see no reason Riley can't earn a promotion to AAA this year. When the BABIP drops, and subsequently his production, we should be looking for his BB rate to stay in the 9% range and his K rate to stay in the low 20s. As long as those numbers stay in line with expectations, it doesn't really matter what his BABIP or OPS end up being in AA (within reason, of course).
Decision makers in modernized FOs are not concerned with his OPS when determining promotions, that's for sure. They are looking at swing rates, contact rates, exit velocities, launch angles, and other data that directly measure player skill. These are all data we don't have access to for minor leaguers, unfortunately, but the teams do.
Once he's in AAA he's an option for the MLB team. I'm sure he's an option for early 2019, which is why they didn't sign another option at 3B this year.